OAL is used for the loaded cartridge with the bullet in it. I assume you mean case length.
A normal 45-70 case is 2.100".
I don't personally use the shorter Hornady cases but that's because I have a few hundred Win/Rem/Starline cases. If I didn't have anything else I would use them.
There are two philosophies with the shorter Hornady 45-70 cases:
1. Load to the manuals OAL, ignoring the shorter brass. This will leave more of the bullet shank exposed but will leave the correct amount of space in the case. You can use the same load data as normal length brass. The crimp groove will be outside the case so I wouldn't use these for a tube magazine like in a lever rifle.
2. Seat the bullet to the crimp groove and crimp as normal but work up a separate load for the shorter Hornady cases. This will leave less room inside the case so higher pressures will be produced with the same powder charge. You would need to work up separate loads for different length cases if you did this.
In a lever rifle, I'd use #2, in a single-shot or box mag fed rifle, I'd use #1.
Some die sets can't be adjusted far enough down to crimp the shorter cases. I believe RCBS can but I'm not sure about other brands.
That's only if I was forced to use the shorter Hornady cases. I'd just order some Starline 45-70 cases from Budget or The Bullet Barn before that.
I have had issues with Hornady Leverevolution brass before. The 30-30 stuff I was trying to reload had pistol-depth primer pockets. Rifle primers would stick out something terrible but shorter large pistol primers would seat flush (I tried one just to test). I thought about deepening the pockets but just tossed the brass in the scrap bin since I have hundreds of regular 30-30 cases (Win, Rem, Fed, etc.). I don't know if the 45-70 cases suffer from the same issue.
